Time?

There may be 100 threads about this, but can someone logically explain "time" in chess? 

So... I understand losing time in development - moving a piece twice in the opening, being X number of moves ahead or behind when it comes to connecting rooks, etc. But where I lose the concept of time entirely is in the middle game. When I watch analysis, they often say "this move loses time"... but relative to what?

I mean, I get that some moves don't do anything - making it sort of a wasted move, and other attacking moves put your pieces on better squares while putting your opponents on worse ones (although "how do you know good and bad squares" is another question coming soon), but can't one well played tactical move, or one blunder, or one missed move,  throw the whole concept of how much time was previously gained or lost out the window, because now the other player - previously behind in "time"- is now on the attack? 

How do you even know where you are with time in the middle game - what is it measured against? How do you know what gains or loses time? And most specifically, how can you tell before a move what it does relieve to  "time"?

In the middle game. It is assumed that both players have a plan to improve their position. Whoever can complete their plan the quickest, will have more time to waste by doing other stuff. 

If you waste a move that does nothing then you have lost time as it will take longer for you to complete your plan.

An endgame is the easiest way to describe this.

Thank you @ gingerninja2003

So, I can certainly understand the end game example you gave. I get why the right moves matter greatly when there are only so many left in the game.

But... the analysis I often see has way more pieces on the board, and a lot of moves left in the game - and any one of them seem like they could turn the tides. When each side is castled and still has like 10 pieces, how do you know what "time"is, and whose ahead in it?

Heres a recent example I saw: with one rook each (no queen or minor pieces), and an even number of pawns on the board, white's rook on e7 was attacked by the black king moving to d8, and had to retreat to, say e4. The analyst said " this costs white time" ... but why? what is the "time" that is lost? the rook still controlled the only open file with quite a bit of range ... I mean, obviously you could be using that turn to do something else, but the opponent used a turn to attack a piece that was only going to move anyway, so how is that not more or less a wash?

Then, what does "time" do for you as pieces are moving all over the place? I keep hearing it's super important, but when it's not super obvious, I don't really see what moves gain or lose it. 

That basically answered the original question. Time is wasted or not wasted depending on whether the move contributes to your plan or goal.  

In this example, the WR is likely to be attacking Ps on the 7th rank, so winning these Ps could be White's plan or goal. When the R has to retreat to e4, it serves less purpose on the 4th rank, hence it wasted time to move it there. If instead, Re4 (say) wins a piece on the 4th rank, then this move achieves a better goal and obviously wouldn't be a waste of time.

6.a7 Kc7?? 1-0